Slow Cooker

A slow cooker, also
called a Crock-Pot, is a cooking device
consisting of a pot (typically 10 in (25 cm) across and
similarly high) made of fired clay and usually glazed,
surrounded by a housing, usually metal, containing a
thermostatically controlled electric heating element. The
ceramic pot, often referred to as a crock, acts as both a
cooking container and a heat reservoir. Many slow cookers
have two settings for power. Slow cookers have loosely
fitting lids (often of glass or similar material) to
retain moisture and heat.

Cooking in these
appliances is done at atmospheric pressure since the lid
is not pressure-tight (and indeed is 'sealed' only by
condensed vapors and gravity); thus, as long as liquid
(usually water, stock, wine or a mixture) remains in the
pot, internal temperatures can go no higher than the
boiling point of the fluid (212�F or 100�C for water at
sea level).

The physics of boiling
prohibit a temperature of the contents above the boiling
point while there is still liquid changing into vapor
(most of which condenses back into the crock and so
returns moisture to the contents). In this respect, a slow
cooker is very different from a pressure cooker, which,
though it also cooks using vapor, has both elevated
pressures (steam in this case) and temperatures.

There is some danger of
explosion from the increased pressure, which is why
maintenance of the pressure relief valve is critical for
pressure cookers; in contrast, no correctly used slow
cooker can explode since no increase in internal pressure
occurs. The outside temperature of a slow cooker can be
expected to exceed the boiling point of water to
facilitate heat transfer to the crock and to the food.

In use, the food is
placed inside the pot and covered with liquid, the lid is
applied, and the unit is switched on. Cooking times vary
with the recipe and with the food quantity, but are
typically several hours. Temperatures are low compared to
traditional ovens used for broiling (typically 600°
F or
320° C or higher) and baking (typically 300 to 500°
F or
150 to 260° C). Cooking is sufficiently slow that, if the
food is not removed promptly at the specified time, little
harm is done.

The liquid and its proper
level is important, for it serves both as the heat
conduction mechanism between the pot walls and the food,
and as the flavoring (herbs and spices) distribution
method and a 'basting' mechanism. No stirring is required
(or recommended) since removing the lid during cooking
causes significant cooking delays. The lid is important as
it prevents escape of hot vapor which would, if permitted,
lead to lowering the internal liquid level, loss of heat
and drying out of the contents.

Recipes for these cookers
must be adjusted to compensate for the nature of the
cooking: often water must be decreased. Some come with
recipe booklets; many cookbooks with slow cooker recipes
are available and there are numerous recipes on the Web. A
small number of cookbooks seek to make complete dishes in
a slow cooker using fewer than five ingredients while
others treat the slow cooker as a serious piece of
culinary equipment capable of producing gourmet
meals.

With some experience,
timings and recipe adjustments can be successfully made
for many recipes not originally intended for these
cookers. The long, moist nature of the cooking method
allows for lower quality cuts to be used.

Product Name

The slow cooker is also
known as a Crock Pot, a registered trademark of
Rival Industries, which developed the modern device. The
names 'slow cooker' and 'Crock Pot' are used
interchangeably in descriptions and recipes, though Rival
is the only producer authorized to use the Crock Pot name,
and usually protects the trademark so that the term
doesn't become a generalized trademark, the way aspirin
and cola have.

The 'Crock Pot' name has
been licensed to ConAgra by Rival beginning in 2004, when
their Banquet frozen food brand introduced a line of
prepared frozen meals called Crock Pot Classics,
which consist of a full four or five-serving meal packaged
and flash frozen by Banquet, then cooked with minimal
preparation in a slow cooker.

The Crock Pot Classics
meal kit includes the meat, vegetables, sauces and
potatoes needed for preparing the meal; water is the only
other item needed. Several varieties, such as stroganoff,
beef stew, and chicken and dumplings are available, and a
trial coupon for the product is usually included in a new
'Rival Crock Pot'.

Food safety

Using a slow cooker,
temperatures are lower than in many other cooking methods,
and cooking times are lengthy. Because of this, some
people have been concerned about the growth of
micro-organisms. Slow cookers are capable of boiling their
contents. Boiling is sufficiently hot to cook all meats,
including poultry, which requires the highest internal
temperature to be safe for consumption.

If the temperature
control mechanism is working correctly, and if food is not
left to stand more than briefly at room temperature, there
are few problems. Filling the pot, adding water, and then
promptly turning on the unit will avoid such problems as
well.

If the starting food
ingredients are frozen, it may take a long time for the
pot to reach proper cooking temperature. During this slow
heating, microbes in the food can multiply. The microbes
will eventually be killed before the food is served, and
so themselves pose little risk. But some microbes produce
toxins which remain even after the microbes have
died.

Most such toxins are
proteins which are destroyed by the heat of cooking, but
some such toxins cannot be destroyed by cooking - for
example, botulism toxin. In practice, most such heat
resistant toxins, including those that cause botulism, are
produced by anaerobic microbes which cannot survive in the
presence of atmospheric oxygen. Heat also kills these
organisms. As with any cooking technique, when cooking
frozen food, do not defrost at room temperature.

A safer technique is to
defrost ingredients in a cold environment, usually a
refrigerator, where the temperature is too low for the
microbes to thrive. Alternatively, one may defrost foods
using a microwave oven so that the bacteria have little
time to grow.

Perpetual stews should
not be maintained in slow cookers, as slow cookers do not
typically provide sufficient heat to compensate for
frequent additions and removals of food; nor do they cook
quickly enough to cook newly added food thoroughly before
the next withdrawal becomes likely. This relatively slow
recovery of temperature after an addition or withdrawal
may cause safety problems. Removal of the lid lets heat
and moisture escape, prolonging cooking time and giving
microbes the chance to grow.

Other Hazards

Because these cookers are
portable/movable, contain large quantities of hot food and
water, and because they are left unattended during long
cooking times, they are dangerous around small children
and exploratory pets. Cooking areas should be blocked off
� effectively � if either might be present without
responsible supervision.

Like all electrical
appliances, failures (in the electrical wiring or the
control mechanisms) can cause problems, including fires.
Although slow cookers have few parts that could fail and
reports of their failures are rare, unattended slow
cookers should be nonetheless treated with respect and
caution.

For instance, they are
best used in a kitchen placed on a tile or similarly
reduced flammability surface, and not near flammable
materials such as papers or flammable fluids since the
outside of the slow cooker does become warm during
operation. The fire risk is certainly minimized by
isolating the appliance from surrounding flammables.